Oscillator system



-Aug. 8, 1939. J. B. DOW

OSCILLATOR SYSTEM Filed July 5; 1951 2 Sheets-Sheet 1 15k I I'I I I IJ II qwENToR germ:

7155 .5. Dow

ATTORNEY Aug. 8, 1939. J. B. DOW

OSCILLATOR SYSTEM 2 Sheets-Sheet 2 Filed July 5, 1931 lflVENTOR Jenn mgs.5. Dow

ATTORNEY Patented Aug. 8, 1939 UNITEIS STATES PATENT OFFICE 28 Claims.

(Granted under the act of March a, 1883, as amended April so, 1928; :mo. e. 751) My invention relates broadly to oscillator systerns and moreparticularly to a constant frequency electron tube oscillator system.

One of the objects of my invention is to pro- .5 vide a precision typeoscillator which is capable of delivering a large amount of usefulenergy.

Another object of my invention is to provide a precision type oscillatorwhose frequency stability is relatively free from the influence ofattached circuits.

A further object of my invention is to provide an oscillator circuit,the output portion of which is electrically independent of the frequencydetermining portion.

A still further object of my invention is to provide means forelectrostatically shielding those tube elements which are directlyassociated with the generator portion of the circuit from an element ofthe tube which is utilized only to derive energy from the system.

A still further object of my invention is to provide means formaintaining certain elements of the oscillator tube at relatively largehigh frequency potentials with respect to ground and at the same time,avoiding the use of choke coils which, when employed at the very highfrequencies, introduce design diiilculties.

Other and further objects of my invention will' be understood from thespecification hereinafter 30 following by reference to the accompanyingdrawings, in which: 1

Fig. 1 discloses a circuit embodying the principles of my invention;Fig. 2 shows a modified form of circuit; and Figs. 3 and 4 show stillfurther modified forms of the circuit of my invention.

In electron tube oscillators of the two anode type, where one anode ofthe tube is associated in circuit with certain other elements of thetube for the generation of oscillations, and a second anode of the tubeis associated in circuit to derive energy from the system, I have foundit essential to electrostatically shield that anode associated with theoutput circuit from those elements of the tube involved in theoscillation generating portion of the system in order that the frequencyof the generated oscillations will not be materially influenced bychanges inthe electrical constants of the output circuit caused bytuning adjustments, reaction from attached circuits, etc. ;One method ofaccomplishing this shielding consists in introducing a separateelectrostatic shield element within the tube in the manner disclosed inmy copending application Serial No. 515,129, filed February 11, 1931.

In the present invention I dispose the output circuit of the systembetween the second anode and the anode structure of the oscillationgenerator, instead of placing the output circuit between the secondanode and cathode. This per- 5 mits the anode structure of theoscillation generator to function as an electrostatic shield to isolatethe second anode, which is associated only with the output circuit, fromthe remaining elements of the tube which are associated with theoscillation generating portion of the circuit.

In electron tube oscillators which utilize three elements of the tubeand their external circuits for the generation of oscillations, it iscustomary to so arrange the circuit that the cathode 15 is at a lowpotential with respect to the shield box or ground in so far as thegenerated high frequency potentials are concerned. This practice hasresulted fromthe fact that any other arrangement of the circuit,whichrequires the cathode to assume high frequency potentials with respect toground, requires also that the cathode heating source be isolated bysuitable choke coils or equivalent devices. It is a well known fact,however, that anyone of the three tube elements of such oscillatorcircuits, may be maintained at substantially zero potential with respectto ground in so far as the generated high frequency potentials areconcerned, provided that the other two elements are permittedto assumewith respect to ground, such high-frequency potentials as they may.

In the circuit of my present invention, I prefer to tie the anode of theoscillation generator to ground or what in effect is the same thing, totie it to the metal box enclosing the circuits. At the same time, I soarrange the circuit that the cathode and grid elements may assume anydesired high frequency potentials with respect to ground. The anodewhich I employ has a screen- 0 like structure so that electrons from thecathode, or electrons resulting from secondary emission from that anodemay pass on to the second anode which is associated with the outputcircuit of the system. The screen-like anode, by virtue of its lowimpedance connection to the metal box or to ground, acts to overcome thecoupling effects of distributed capacity in the circuit and at the sametime so divides the circuit of the generator and output that thescreen-like anode effectively removes the other coupling effects due tointerelement capacities. By means of such a structure, those impedancesin the output circuit and those in the generator are uncoupled to suchan extent that they are substantially independent.

The fact that the grid and cathode elements of the oscillationgenerating portion of the circuit are electrostatically shielded fromthe second anode which is associated with the output circuit, serves toso isolate the output circuit that reaction caused by changes in theelectrical constants of the output circuit has only a quite negligibleeffect upon the frequency of oscillation.

Fig. 1 shows one form of circuit incorporating the principles of myinvention in which I is an electron tube including a grid element 2, acathode element 3, a screen-like anode element 4, and a second anodeelement 5. Grid capacitor 8 and leak I are shown connected between thegrid 2 and inductance coil 8. Inductance coil 8 in combination withcapacitor 9 form a resonant circuit H), which is employed with the grid2, cathode 3, and screen-like anode 4, for generating electricoscillations the frequency of which is substantially determined byresonant circuit l8. Either the inductance 8 or capacitor 9 or both, maybe made variable for adjusting the frequency of oscillation. One end ofinductance coil 8 is connected to ground I I. By virtue of blockingcapacitor l2 whose impedance at the frequency'of oscillation may bechosen as small as desired, the screen-like anode element 4 is virtuallytied to ground. Cathode element 3 is heated by battery l3. Theinductance 8, in the case of Fig. 1, consists of a hollow conductorenclosing conductor l4 which connects one terminal of the cathode 3 withbattery l3. The other terminal of cathode 3 connects to battery l3through the hollow conductor itself which serves jointly as inductance8. Tap connection I5 to battery i3a supplies the screen-like anode 4 atthe necessary potential. By-pass capacitors are shown at l6 and H. Thesecond anode 5 connects through inductance 18 to battery l3a forsupplying the desired potential to anode 5. Inductance 18 in combinationwith capacitor i9, form a second resonant circuit 28 which may be tunedto the frequency at which the generating portion of the circuit isoscillating or to a harmonic of that frequency. This second resonantcircuit serves as an output circuit for the system. If the circuit ofFig. 1 is employed as a master oscillator for a radio transmitter, Ihave found it convenient to connect subsequent stages of the transmitterat 2| and 22 for deriving energy from the oscillator system.

As the second anode 5 is electrostatically shielded from grid 2 andcathode 3 by the screenlike anode 4, any reaction across leads 2| and 22or reaction due to changing the electrical constants of resonant circuit20, has a negligible effect upon the frequency of oscillation determinedby resonant circuit ill in the oscillation generating portion of thecircuit. By tracing the high frequency current path between cathode 3and screen-like anode 4, and the path between second anode 5 andscreen-like anode 4, it will be observed that no common impedance existsacross which a high frequency current in one path could introduce apotential into the other path. The only common portions of thesecircuits are by-pass condensers such as l2, the reactance of which ismade negligible at the frequency of oscillation. The absence of animpedance common to the above mentioned paths and the screen-like anodestructure 4 makes the generator circuit independent of the output orwork circuit 28. Moreover, the above mentioned circuit between cathode 3and screen-like anode 4 and the circuit between second anode 5 andscreen-like anode 4 are not coupled, and for best results thearrangement of these circuits should be such that any reactive elementsin one circuit should be separated from corresponding parts of the otherso that the coeflicient of coupling between these two circuits issubstantially zero. Under these conditions the transfer of energy fromthe generator portion to the output portion takes place only through theelectron stream, and the generator portion of the system is almostwholly independent of reaction from the output circuit.

The oscillation generating portion of the circuit of Fig. 1 serves togenerate oscillations at a predetermined frequency and controls the flowof electrons from the cathode 3 through the screen-like anode 4 to thesecond anode 5. Owing to the division of the electric field betweenscreen-like anode 4 and cathode 3 from the elec tric field betweensecond anode 5 and screenlike anode 4, the latter'anode acts just asthough it were a cathode which emitted pulses of electrons into thefield between the two anodes at a frequency determined by the generator.Experience with the system indicates that the high velocity electronsfrom cathode 3 in striking the screen-like anode 4 also cause secondaryemission from anode 4 and that a portion of the space current to thesecond anode 5 may be due to electron emission from screen-like anode 4.It has been observed in support of this that under certain conditions,the current through tap connection l5 to screen-like anode 4 completelyreverses itself.

The inductance 8 of Fig. 1 which serves both as a portion of theresonant circuit I0 and as the means for supplying cathode heatingenergy from battery I3, may take many forms of construction. It may bein the form of a metallic tube as shown, or may take the form of a Ushaped conductor whose sectional boundary includes return conductor I4for supplying cathode heating energy.

A modified arrangement of the circuit of my invention is shown in Fig. 2in which reference characters I, 2, 3, 4, 5, 6, 1, 9, 10, M, i2, 13, Ba,l5, l8, l1, l8, 2| and 22, correspond to similar portions of the circuitof Fig. 1. The inductance 23 in resonant circuit in of Fig. 2 consistsin part of two parallel conductors for supplying the necessary cathodeheating energy from battery i3. These two conductors are denotedrespectively by reference characters 24 and 25. It will be noted thatblocking capacitors 26 and 21 serve also to close the resonant circuiti0 and thus serve as'a portion of resonant circuit iii. In the circuitof Fig. 2, inductance I8 is employed alone in the output circuit in lieuof a resonant circuit as shown by reference character of Fig. 1.

In the circuits of Figs. 1 and 2, the grid and anode portions of thegenerator circuit are coupled to satisfy the required circuit conditionsfor oscillation, by the two sections of the inductance of resonantcircuit III which is divided by the cathode. Fig. 3 is a furthermodified form of the system of my invention in which the resonantcircuit 28, consisting of the inductance 29 and the capacitor 30, fixesthe frequency of oscillation. In this case, the circuit conditionrequired for oscillation is satisfied by coupling the grid circuitinductively by auxiliary inductance 3| to the inductance 29 of resonantcircuit 28. The screenlike anode 4 of Fig. 3 is connected to ground Hthrough the low impedance blocking capacitor l2. By-pass capacitor 32 isconnected as shown.

In the circuit of Fig. 3, the cathode 3 is heated by battery I! throughinductance, 29 and its contained conductor It. The output circuit anode5 of Fig. 3 is connected through resistor 33 to battery I30 forsupplying anode I at the desired frequency.

' ary of choke coils 34 and 35.

potential. i

While I have shown a resonant circuit 20 in the output circuit of Fig.1, an inductance la in the output circuit of Fig. 2 and fa resistor 33in the output circuit of Fig. 3, any of these impadances may be employedin all three circuits illustrated.

Fig. 4 shows a still further modified form of the circuit of myinvention in which the cathode is heated by battery l3 through theintermedi- It will be noted that the grid capacitor 6 and leak l areshown in a different position than in the'preceding figures. When in theposition shown in Fig. 4, it is desirable to make capacitor 6sufficiently large as to have a very low impedance at the oscillatorSplit capacitor 36 and. inductance 31 form resonant circuit 38 which isadjusted to the frequency of oscillation desired.

While particular mention has been made of the use of the system of myinvention for the generation of high frequency currents, it will beunderstood that by suitable choice of circuit constants, low frequencycurrents may also be produced The term high frequency is thereforeintended to be a generic one including either high or low frequencyinsofar as my disclosure .and claims are concerned.

The following observational data made upon the circuit basically illusrated in Fig. 4 are of interest. These data were observed when theoscillation generating portion of the circuit was tuned to a frequencyof approximately 2000 kilocycles. A conventional type of four elementelectron tube rated at 75 watts output was employed. Resonant circuits38 and 20 were shielded from each other to prevent undesirable coupling.A visual type of beat frequency indicator having a measurement precisionof one cycle in a million was employed in making these observations:

(a) Tuning circuit 20 through resonance at the fundamental frequencycauses the frequency of oscillation to shift 0.005 per cent.

(b) Tuning circuit 20 through resonance at the second harmonic of thefundamental frequency causes the frequency to shift 0.0015 per cent. 1

(0) With second anode element 5 supplied at 1200 volts and screen-likeanode 4 supplied at 500 volts, the output in radio frequency energy atboth the fundamental and second harmonic frequencies, is more than ampleto fully excite a similar electron tube employed as a radio frequencyamplifier.

(d) Changing the voltage supply to second anode 5 and screen-like anodel by 20 per cent, causes the frequency to change 0.0005 per cent.Changing these voltages 50 per cent, causes the frequency to change0.0013 per cent.

The preceding data serve to indicate the effectiveness of the system ofmy invention in meeting the need for a circuit combining high output andprecision as to frequency stability.

While I have described my invention in certain preferred embodiments, Idesire that it be understood that modifications may be made and that nolimitations upon my invention are intended other than are imposed by thescope of the appended claims.

The invention described herein may be manufactured and used by or forthe Government of the United States ,of America for governmental.

purposes'without the payment of any royalties thereon or therefor.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is as fol- 2. A system for the production of high frequencyenergy having a generator comprising an electron tube having a cathode,anode and control electrode, sources of potential for energizing saidelectrodes, a resonant circuit, said resonant circuit including ahollowtubular inductance apertured intermediate the ends thereof, an insulatedconductor extending through the tube of said inductance, connectionsbetween one of said sources of potential to said inductance and to saidinsulated conductor, and connections from said cathode to saidinductance and to the conductor therein through the apertured por-' tionof said inductance, in combination with an auxiliary element in ,theelectron stream of said generator in said tube and an output circuit forsaid system disposed between said auxiliary element and said anode, andmeans including said anode electrode for electrostatically shieldingsaid cathode and control electrode from said auxiliary element.

3. In a system in which a cathode and two other electrodes of anelectron tubeare employed for the generation of high frequency energyand a fourth electrode is used inconnection with an output circuit fortaking off said energy, the method of minimizing changes in frequencydue to changes in the electrical constants of said output circuit, whichconsists in substantially shielding the electron stream of the generatorportion of said system from the influence of high frequency potentialson said fourth electrode and in maintaining one of said two otherelectrodes at substantially zero high frequency potential with respectto ground.

4. An alternating current source having a generator comprising at leastthree elements of an electron tube and interconnecting externalcircuits, in combination with a tube element additional to those forminga part of said generator, means including one of said first mentionedelements for substantially shielding the electron stream between theelements of said generator from the alternating component of theelectric field of said additional element, and an output circuitdisposed between the element of said means and said additional element.

5. A generator of high frequency oscillations comprising a cathodeelement, control element and screen-like anode element of an electrontube arranged with external circuits and sources of supply potential forthe generation of oscillational to those forming a part of saidgenerator,

means including said screen-like anode element for substantiallyshielding said control element from the high frequency component of theelectric field of said additional element, and an output circuitdisposed between said additional tube element and said screen-like anodeelement.

6. A source of high frequency energy having an electron tube includingoscillation producing elements, circuits interconnecting the oscillationproducing elements of said tube and a power supply and comprising anoscillation generator, in combination with an additional elementpositioned in spaced relation to one of said oscillation producingelements so as to be in the electron stream of said generator, a circuithaving variable electrical constants interconnecting externally of saidtube said additional element and the element in spaced relation to whichit is disposed and means including the last mentioned element forelectrostatically shielding the electron stream between said oscillationproducing elements from high frequency variations of potential of saidadditional element.

7. A source of high frequency energy having an electron tube thecathode, control electrode and grid-like anode of which in combinationwith external circuits constitute an oscillation generator, a powersupply connected to said circuits for the generation of oscillations, anadditional electrode positioned in said tube in the electron stream ofsaid generator, high frequency output means for said source disposedbetween said additional electrode and said grid-like anode and meansincluding said grid-like anode for substantially electrostaticallyshielding said control electrode from said additional electrode for highfrequency potential variations existent across said output means.

8. A source of high frequency energy in accordance with claim 7 in whichsaid oscillation generator is regenerative.

9. A source of high frequency energy according to claim '7 in which saidpower supply is so connected to the electrodes of said tube as to rendersaid additional element electro-positive with respect to said cathode.

10. A source of high frequency energy accord ing to claim '7 in whichsaid power supply is so connected to the electrodes of said tube as torender said additional element electro-positive with respect to saidgrid-like anode.

11. A source of high frequency energy having a generator comprising anelectron tube including cathode, control and anode elements and circuitsincluding a power supply interconnecting said elements for thegeneration of oscillations, a resonant circuit cooperating with saidcircuits for determining the frequency of oscillation of said generator,said resonant circuit comprising at least in part a multiple conductorinductance, means for heating said cathode, said means comprising acircuit from said power supply through two conductors of said inductanceto-said oath-- ode, in combination with an auxiliary element in theelectron stream of said generator and an output circuit for said sourcedisposed between said auxiliary element and said anode element. andmeans including said anode element for electrostatically shielding saidcathode and control elements from said auxiliary element.

12. A source of high frequency energy according to claim 11 in whichsaid auxiliary element is electropositive with respect to said cathode.

tions, in combination with a tube element addi- 13. A source of highfrequency energy according to claim 11 in which said auxiliary elementis electropositive with respect to said anode.

14. A source of high frequency energy according to claim 11 in whichsaid multiple conductor inductance comprises a tubular conductorenclosing a second conductor which is insulated therefrom.

15. An electron discharge apparatus including at least one electron tubeand having an oscillation generator circuit includinggenerator-electrodes in the discharge path of said tube, in combinationwith an additional circuit connecting one of said generator-electrodeswith an addtional electrode in said discharge path, and means includingthat one of said generator-electrodes last mentioned whereby theremaining generator-electrodes in said tube are substantially shieldedfrom said additional electrode for potential variations across saidadditional circuit of frequency corresponding to that for which saidoscillation generator circuit is adjusted.

16. An electron discharge apparatus in accordance with claim 15 whereinsaid additional circuit comprises at least in part a resonant circuit.

17. A source of high frequency energy comprising an electron tube havinga cathode, control electrode, grid-like anode and an additional elementarranged in the order named, a resonant circuit and a source ofpotential interposed between said cathode, control electrode andgridlike anode to provide an oscillation generator, an output circuitfor said source interposed between said additional element and at leastone of the elements included in said oscillation generator, and meanscomprising a path of low radio frequency impedance connected betweensaid grid-like anode and ground for maintaining the grid-like anode atsubstantially zero high frequency potential whereby said grid-like anodeelectrostatically shields the remaining electrodes comprising saidoscillation generator from said additional element.

18. A source of high frequency energy in accordance with claim 17wherein said output circuit includes a resonant section.

19. Asource of high frequency energy in accordancwith claim 17 whereinsaid output circuit includes a resonant section tuned to a frequencyharmonically related to the frequency generated by the oscillationgenerator.

20. An electron discharge apparatus including an electron tube having acathode element, control element, grid-like anode element, and anadditional element positioned in the order named, means for maintainingsaid control element, said grid-like anode element, and said additionalelement at predetermined potentials with respect to said cathodeelement, a circuit connecting said cathode and control elements, asecond circuit connecting said cathode and gridlike anode elements,means for regeneratively coupling said circuits, an output circuitdisposed between said grid-like anode element and said additionalelement including a portion of said second circuit, said output circuitbeing substantially reactanceless at the frequency for which said firstcircuits are regenerative over that portion of said output circuit whichis common to said second circuit.

21. An electron discharge apparatus including an electron tube having acathode element, control element, grid-like anode element, and anadditional element positioned in the order named, means for maintainingsaid control element, said grid-like anode element, and said additionalelement at predetermined potentials with respect to said cathodeelement, a circuit including an impedance connected between said cathodeelement and control element, a second circuit including an impedanceconnected between said cathode element and said grid-like anode element,means for regeneratively cou-' pling said circuits, an output circuitincluding a tuned resonant circuit and a portion of said second circuitdisposed between said grid-like anode element and said additionalelement, said output circuit being substantially reactanceless at thefrequency for which said first circuits are regenerative over thatportion of said output circuit which is common to said second circuit.

22. An electron discharge apparatus including an electron tube having acathode element, control grid element, and grid-like anode elementpositioned in the order named, means for rendering said cathode electronemitting and means for maintaining said grid-like anode ele- -mentelectro-positive with respect to the cathode element, a circuitincluding-an impedance connected between said cathode element and saidcontrol grid, a second circuit including an impedence connected betweensaid cathode element circuit which is common to said second circuit.

23. An electron discharge apparatus including an electron tube having acathode element,

control grid element, and a grid-like anode element positioned in theorder named, means for rendering said cathode elementelectron emittingand means for maintaining said grid-like anode element electro-positivewith respect to the cathode, acircuit including an impedance connectedbetween said cathode element and said control grid element, a secondcircuit including an impedance connected between said cathode elementand said grid-like anode element and means for coupling said first andsecond circuits whereby an oscillation generating means is provided, anadditional element in said tube adjacent said grid-like anode elementand;

on the side thereof opposite said control grid element and an outputcircuit including a tunable resonant section and a .portion of saidsecond circuit disposed between, said additional element and saidgrid-like anodeelement, said output circuit being substantiallyimpedanceless at the frequency of oscillation of said oscillationgenerating means over that portion of said output circuit which iscommon to said second circuit and means for maintaining said additionalelement el'ectro-positive with respect to said cathode element.

24. A regenerative oscillation generator circuit comprising an electrondischarge device characterized by high internal resistance having acathode, anode, control grid and screen grid, a tuned input circuitcoupled between said control grid and cathode, a tunedoutput circuitconnected between said anode and screen grid, a coil inductively coupledto said input circuit and hav- -ing one terminal connected to thecathode and the other terminal connected to the screen grid end of saidoutput circuit whereby the currents in said screen grid and anodecircuits additively combine in said coil to affect regeneration.

25. An oscillation generator having an electron tube provided with acathode, a control element, an inner anode and an outer anode, anoscillation generating circuit comprising said cathode, control elementand inner anode, an output circuit connected at one side thereof to saidouter anode and at the other side thereof to said inner anode, wherebysaid inner anode is common to both circuits, and means for maintainingsaid inner anode at radio frequency ground potential for isolating saidcircuits from each other.

26. In a radio system, the combination of an electron tube having anode,cathode and grid electrodes, means for heating said cathode, an inputcircuit connected across said cathode and grid electrodes to vary thepotential of said cathode at a high frequency rate, and means comprisingradio frequency choke coils for preventing said high frequencyvariations from affecting said cathode heating means.

27. In a radio system, the combination of an electron tube having anode,cathode and grid electrodes, means for heating said cathode, an inputcircuit connected between said-cathode and grid to vary the potential ofsaid cathode at a high frequency rate, and radio freqdency choke coilsbetween said cathode and said heating means to maintain a high inputimpedance to said tube.

' 28. Oscillation generating means comprising, a sealed vitreouscontainer, an emission element therein, a plurality of cold electrodesin said container, said cold electrodes being spaced a differentdistance from said emission element, a frequency determining oscillationcircuit connected between a pair of said cold electrodes and to saidemission element, an oscillation circuit connected between another ofsaid cold electrodes and said emission element, means for applyingdirect current charging potential to said electrodes, 'the value of thepotential applied to the electrodes connected with said, last namedcircuit being greater than the potential applied to the other electrodeswhereby oscillations of greater amplitude appear in said circuit, themaximum amplitude of the oscillations appearing in said frequencydetermining circuit being greater than the minimum amplitude of theoscillations appearing in -said other circuit wherebythe intensity ofthe current flowing in said other circuit alters at a rate greater thanthe frequency to which the frequency determining circuit is tuned, andmeans fon tuning said other circuit to a harmonic of the frequency ofthe, I

